Wafer polishing machine

ABSTRACT

A CMP machine of the invention includes first and second polishing bases  14  and  15,  first and second wafer holding heads  31  and  32,  a wafer loading unit  41,  a wafer unloading unit  42,  first and second head rotating mechanism rotating the first and second wafer holding heads so as to position then above the first and second polishing bases, wafer loading unit, or wafer unloading unit, a first transportation mechanism transporting an unpolished wafer to the wafer loading unit, and a second transportation mechanism, transporting a polished wafer from the wafer unloading unit. The first and second polishing bases are located mutually adjacently, the wafer loading unit and wafer unloading unit are located mutually adjacently, the first polishing base and wafer loading unit are located diagonally, the second polishing base and wafer unloading unit are located diagonally. Owing to this structure, transportation of a wafer to the wafer loading unit and transportation of a wafer from the wafer unloading unit are achieved by the different transportation mechanisms. This leads to a minimized adhesion of dust to an unpolished wafer.

TECHNICAL FIELD

The present invention relates to a wafer polishing machine. Moreparticularly, this invention is concerned with a wafer polishing machineadopting a chemomechanical polishing (CMP) process effective inflattening the surface of a wafer in the course of drawing IC patternson the wafer.

BACKGROUND ART

Microscopic machining of ICs has been facilitated in recent years. ICpatterns are drawn on many layers. It is therefore unavoidable that someirregularity occurs on the surfaces of the patterned layers.Conventionally, even when such irregularity occurs on one layer, asubsequent layer is patterned with the irregularity left intact. As thenumber of layers increases, the widths of lines or the diameters ofholes diminish. This makes it hard to draw fine patterns. Defect canoccur frequently. For this reason, after the surface of a patternedlayer is polished to be flat, the next layer is patterned. Moreover,after holes are bored, a metallic layer for linking layers is formed byperforming plating or the like. The metallic layer on the surface of thepatterned layer is abraded so that the metallic layer will be left onlyin the holes. A wafer polishing machine (CMP machine) adopting the CMPprocess is used to polish wafers in the course of drawing IC patterns.

FIG. 1A and FIG. 1B are explanatory diagrams concerning machining to beperformed according to the CMP process in the course of manufacturingICs. FIG. 1A shows polishing of the surface of an interlayer dielectricto be performed so that the surface thereof will become flat. FIG. 1Bshows abrasion of the surface thereof to be performed so that a metalliclayer will be left in holes alone. As shown in FIG. 1A, after a pattern2 is drawn on a substrate 1 by forming a metallic layer or the likethereon, when a dielectric interlayer 3 is formed, the pattern portionof the dielectric interlayer becomes higher than the other portionthereof. This results in an irregular surface. A CMP machine is thenused to polish the surface. The surface is thus brought to the stateshown in the right side of FIG. 1A. Thereafter, the next pattern isdrawn. For forming a metallic layer linking layers, as shown in FIG. 1B,connection holes are bored in the lower layer having the pattern 2 drawnthereon, and a metallic layer 4 is formed by performing plating or thelike. Thereafter, the CMP machine is used to fully abrade thesuperficial metallic layer 4.

FIG. 2 shows the basic structure of the CMP machine. As illustrated, theCMP machine has a polishing base 11 and a wafer holding head 21. Anelastic polishing cloth 13 is bonded to the surface of the polishingbase 11. The polishing base 11 rotates with an axis of rotation 12 as acenter. Slurry that is an abrasive is supplied to the polishing cloth 4on the rotating polishing base 1 through a nozzle that is not shown. Thewafer holding head 21 holds a wafer 100 to be polished, presses thewafer against the polishing cloth 13 with a predetermined pressure, androtates with the axis of rotation 22 as a center. The surface of theheld wafer is thus polished. A groove is generally formed in thepolishing cloth 13 in order to facilitate supply of slurry to thecontact surface of the polishing cloth coming into contact with a wafer.In the drawing, the number of wafer holding heads 21 is one. In thiscase, the right side of the polishing base 1 is left unused, andproduction efficiency is unsatisfactory. Generally, a plurality of waferholding heads 21, for example, two or four wafer holding heads 21 areincluded in order to concurrently polish a plurality of wafers.

When the CMP machine is used for polishing, the wafer 100 is firstaligned and transported to a loader. The wafer holding head 21 holds thewafer placed on the loader using a suction mechanism, moves it to thepolishing base 11, and presses it against the polishing base 11. Thewafer is thus polished. When polishing is completed, the wafer holdinghead 21 holds the wafer using the suction mechanism and transports it toan unloader. Slurry that is an abrasive is adhering to the wafer 100transported to the unloader. After the wafer is washed using a washer,it is dried. The wafer is then transported to a wafer collector such asa cassette. After the wafer is polished, IC patterns are drawn on thewafer according to a lithography method or the like. If abrasiveparticles or leavings were left intact, it would cause a defective ICpattern. Washing must therefore be carried out in order to make a wafervery clean. A washed wafer must be handled carefully for fear dust orthe like may adhere to the wafer.

The CMP machine is required to meet such requirements that theperformance in polishing must be high enough to ensure high-precisionpolishing, processing efficiency expressed as a throughput must beexcellent, and an area needed for installation must be small. To meetthe requirements, a plurality of polishing bases is included, and awafer loading unit and a wafer unloading unit are used in common amongthe polishing bases. The wafer loading unit supplies wafers to theplurality of polishing bases. The wafer unloading unit transports wafersfrom the plurality of polishing bases. When this configuration isadopted, since one wafer loading unit and one wafer unloading unit areincluded relative to a plurality of polishing bases, the area needed forinstallation can be made smaller. Moreover, the time required fortransporting wafers from the wafer loading unit to the polishing base orthe time required for transporting wafers from the polishing base to thewafer unloading unit is shorter than the time required for polishing.Even when the above configuration is adopted, the processing efficiencywill not deteriorate. Furthermore, polishing a wafer may be achieved bycombining rough polishing and fine polishing. The rough polishing isperformed at a high polishing speed but is insufficient in precision.The fine polishing is performed at a low polishing speed but ensureshigh precision. When the above configuration is adopted, one of theplurality of polishing bases may be used to perform close polishing, andthe other polishing bases may be used to perform rough polishing.

The CMP machine having a plurality of polishing bases includes the waferloading unit and wafer unloading unit. Nevertheless, the sametransportation mechanism is used to transport wafers to the waferloading unit and to transport wafers from the wafer unloading unit.Therefore, dust such as abrasive particles or leavings adheres to thetransportation mechanism that has transported polished wafers. This kindof dust adheres to wafers that have not been polished and aretransported to the wafer loading unit. The dust adhering to the polishedsurfaces of wafers does not pose a severe problem. However, the dustadhering to the backs of the wafers poses a problem in that a polishingpressure becomes inhomogeneous. This leads to deteriorated performancein polishing.

DISCLOSURE OF THE INVENTION

The present invention attempts to solve the above problems. An object ofthe present invention is to provide a CMP machine having a plurality ofpolishing bases, and a wafer loading unit and wafer unloading unit thatare used in common among the plurality of polishing bases. The waferloading unit supplies wafers to the plurality of polishing bases. Thewafer unloading unit transports wafers from the plurality of polishingbases. In the CMP machine, the components are laid out so that adhesionof dust to unpolished wafers can be minimized.

To accomplish the above object, a CMP machine in accordance with thepresent invention has two polishing bases located mutually adjacently.Moreover, a wafer loading unit and wafer unloading unit are locatedmutually adjacently. A first polishing base and the wafer loading unitare located diagonally. A second polishing base and the wafer unloadingunit are located diagonally. Transportation of a wafer to the waferloading unit and transportation of a wafer from the wafer unloading unitare achieved using different systems.

To be more specific, a CMP machine in accordance with the presentinvention consists of first and second polishing bases, first and secondwafer holding heads, a wafer loading unit, a wafer unloading unit, afirst head rotating mechanism, a second head rotating mechanism, a firsttransportation mechanism, and a second transportation mechanism. Thefirst and second polishing bases each have a polishing cloth attached tothe surface thereof, and rotate the polishing cloth thereof. The firstand second wafer holding heads each hold wafers and rotate whilepressing the surfaces of the wafers against the polishing cloth.Unpolished wafers are placed on the wafer loading unit. Polished wafersare placed on the wafer loading unit. The first head rotating mechanismrotates the first wafer holding head so as to position it above thefirst polishing base, wafer loading unit, or wafer unloading unit. Thesecond head rotating mechanism rotates the second wafer holding head soas to position it above the second polishing base, wafer loading unit,or wafer unloading unit. The first transportation mechanism transportsan unpolished wafer to the wafer loading unit. The second transportationmechanism transports a polished wafer from the wafer unloading unit. Thefirst and second polishing bases are located mutually adjacently. Thewafer loading unit and wafer unloading unit are located mutuallyadjacently. The first polishing base and wafer loading unit are locateddiagonally. The second polishing base and wafer unloading unit arelocated diagonally.

According to the present invention, the first transportation mechanismand second transportation mechanism are included so that transportationof wafers to the wafer loading unit and transportation of wafers fromthe wafer unloading unit can be achieved using the differenttransportation mechanisms. Adhesion of dust to unpolished wafers cantherefore be minimized.

The first and second wafer holding heads are designed to be able torotate mutually independently while holding two respective wafers. Thesurfaces of the polishing bases can thus be used effectively.

One of the two polishing bases may be used for rough polishing, and theother polishing base may be used for fine polishing.

A mechanism for rotating the wafer loading unit and wafer unloading unitor moving them parallel to each other so as to shift them mayconceivably be included. Using the mechanism, either the wafer loadingunit or wafer unloading unit is selectively moved to a position at whichwafers are received from or output to the wafer holding head.Consequently, the mechanism makes it possible to switch the waferloading unit and wafer unloading unit, and to receive or output wafersat the same position. When the mechanism is utilized, three polishingbases may be included and assigned to rough polishing and finepolishing. Two polishing bases are assigned to polishing requiring along processing time. This may lead to an improved throughput. However,according to this configuration, the first and second transportationmechanisms must access the common position, at which wafers are receivedfrom or output to the wafer loading unit or wafer unloading unit, fromdifferent directions. A component for aligning unpolished wafers and acomponent for washing polished wafers must be located in differentdirections. This leads to an increase in the area required forinstalling the CMP machine. In particular, a bay through which wafersare moved in or out of the CMP machine must be widened. This is notpreferable in constructing an automated manufacturing process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A and FIG. 1B are explanatory diagrams concerning processing to beperformed according to a CMP process;

FIG. 2 shows the basic structure of a CMP machine;

FIG. 3 shows the layout of components of a CMP machine in accordancewith an embodiment of the present invention; and

FIG. 4 shows the structure of a wafer holding head in accordance withthe embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 3 is a top view showing the layout of components of a CMP machinein accordance with an embodiment of the present invention. Asillustrated, two polishing bases 14 and 15 are included. Two waferholding heads 31 and 32 each holding wafers and pressing them against anassociated polishing base are placed above the two polishing bases. Thewafer holding heads 31 and 32 include wafer holding and rotatingmechanisms 33, 34, 35, and 36. Each wafer holding and rotating mechanismsucks and holds a wafer. For polishing, each wafer holding and rotatingmechanism pneumatically presses a wafer against a polishing cloth placedon the polishing base 14 or 15. The wafer holding heads 31 and 32 arehung on rotation bars 37 and 38 each having one end thereof supported byan axis of rotation 40 and the other end thereof supported by an annularguide 39. The wafer holding heads 31 and 32 can thus move over a waferloading unit 41 and a wafer unloading unit 42.

Unpolished wafers stowed in a plurality of wafer cassettes 62 are pickedup by a transportation arm 60 supported to be able to move on a movingmechanism 61, and then placed on a relay base 59. A transportation arm58 transports the wafer to a thickness measuring instrument 57 formeasuring and checking the thickness of a layer, to be polished, of thewafer placed on the relay base 59. Wafers whose layer thicknesses havebeen checked are placed on receiver members 43 and 44 on the waferloading unit 41 by the transportation arm 58.

Each of polished wafers placed on receiver members 45 and 46 on thewafer unloading unit 42 is placed on a first washer 51 by atransportation arm 48. The wafer washed by the first washer 51 is placedon an adjoining second washer 52. Washing a polished wafer is achievedby following two steps. The transportation arm 48 transports a waferthat has just been polished, and is therefore smeared. Thetransportation arm 54 transports a wafer that has undergone thefirst-step washing, and is therefore not smeared so much as a wafer onthe transportation arm 48. A wafer having undergone the second-stepwashing in the second washer 52 is placed on a drier 53 by atransportation arm 55 and then dried. The transportation arms 54 and 55are supported to be movable on a moving mechanism 56. The wafer havingundergone the second-step washing is less dirty than a wafer havingundergone the first-step washing. The transportation arm 55 is thereforeincluded separately from the transportation arm 54 for transporting awafer having undergone the first-step washing. A wafer dried by thedrier 53 is returned to the wafer cassette 62 by the transportation arm60.

Polishing is performed in a time lag of a half cycle between twopolishing bases 14 and 15. While the polishing bases 14 and 15 are usedfor polishing, wafers whose layer thicknesses have been checked areplaced on the receiver members 43 and 44 on the wafer loading unit 41.When polishing using the polishing base 14 is completed, the waferholding head 31 holds the wafers in the wafer holding and rotatingmechanisms 33 and 34, and moves clockwise to above the wafer unloadingunit 42. The wafer holding head 31 then places the polished wafers onthe receiver members 45 and 46. The wafer holding head 31 then moves toabove the wafer loading unit 41 and sucks unpolished wafers placed onthe receiver members 43 and 44 into the wafer holding and rotatingmechanisms 33 and 34. Meanwhile, the transportation arm 48 transportsthe polished wafer from the receiver member 45 into the first washer 51.The wafer holding head 31 holds the unpolished wafers and moves to abovethe polishing base 14, whereby polishing is started. In the meantime,unpolished wafers are placed on the receiver members 43 and 44 on thewafer loading unit 41. The wafer having been washed in the first washer51 is moved to the second washer 52. Concurrently, the transportationarm 48 transports the polished wafer from the receiver member 46 to thefirst washer 51.

Thereafter, when polishing using the polishing base 14 is completed, thewafer holding head 32 holds the wafers in the wafer holding and rotatingmechanisms 35 and 36 and moves counterclockwise to above the waferunloading unit 42. The wafer holding head 32 then places the polishedwafers on the receiver members 45 and 46. Thereafter, the wafer holdinghead 32 moves to above the wafer loading unit 41, and sucks unpolishedwafers placed on the receiver members 43 and 44 into the wafer holdingand rotating mechanisms 33 and 34. The other movements are identical tothose mentioned above.

The polishing bases 14 and 15 and the wafer holding and rotatingmechanisms 33, 34, 35, and 36 of the wafer holding heads 31 and 32 mayhave the same structures as conventionally employed ones. Herein, thewafer holding and rotating mechanisms are each structured to press awafer against a polishing cloth using a predetermined pneumaticallyinduced pressure. FIG. 4 shows the structure of the wafer holding androtating mechanism 33 of the wafer holding head 31.

As illustrated, the wafer holding and rotating mechanism 33 includes acarrier member 71, a polished surface adjustment ring 74, a guide ring75, a rotary substrate 77, a rotary guide plate 80, an axis of rotation82, gears 83 and 84, and a motor 85. The axis of rotation 82 has a slipring. The carrier member 71 has air ports 72 through which air is jettedout and suction ports 73 through which a negative pressure is applied. Awafer 100 is pressed against a polishing cloth 13 using the pressure ofthe air jetted out of the air ports 72. A negative pressure is thenapplied through the suction ports 73, whereby the wafer 100 is suckedand held on to the carrier member 71. The polished surface adjustmentring 74 comes into contact with the polishing cloth 13 with apredetermined pressure, and thus homogenizes the state of the innerpolishing cloth 13 so as to prevent irregular polishing. Moreover, whenthe wafer holding head 31 moves upward, the polished surface adjustmentring 74 holds the carrier member 71. For pressing the wafer 100 againstthe polishing cloth 13, the polished surface adjustment ring 74 and thecarrier member 71 are not mutually restricted. When the wafer holdinghead 31 moves upwards, the guide ring 75 holds the polished surfaceadjustment ring 74. For pressing the wafer 100 against the polishingcloth 13, the guide ring 75 and polished surface adjustment ring 74 arenot mutually restricted.

A rubber seat 76 is placed between the rotary substrate 77, carriermember 71, an polished surface adjustment ring 74. A predetermined airpressure is applied through an air port 78, whereby the carrier member71 is pressed down with a predetermined pressure. A predetermined airpressure is applied through air ports 79, whereby the polished surfaceadjustment ring 74 is pressed down with a predetermined pressure. Whenthe carrier member 71 is pressed down with an air pressure appliedthrough the air port 78, the gap between the carrier member 71 and wafer100 varies. Thus, although the pressure of air jetted out through theair ports 72 remains unchanged, the pressure with which the wafer 100 ispressed against the polishing cloth 13 can be varied.

The rotary substrate 77 is held by the rotary guide plate 80 viabearings 81 so that the rotary substrate can rotate. When a motor 85 isrotated, the rotary substrate 77 is rotated via the gear 84 and the gear83 formed on the axis of rotation 82.

The wafer holding and rotating mechanisms 34, 35, and 36 have the samestructure as that mentioned above.

As mentioned above, the CMP machine requires a measuring instrument formeasuring the thickness of a layer of an unpolished wafer, a washer forwashing a polished wafer, and a drier for drying the washed wafer. Whena plurality of polishing bases is included in order to improve athroughput offered by the machine, it is necessary to preventdeterioration of polishing precision caused by dust such as abrasiveparticles or leavings adhering to the back of an unpolished wafer.Moreover, an area needed for installation must be taken intoconsideration. Especially in an automated CMP line, the dimensions of abay required for supplying and collecting unpolished wafers and polishedwafers must be taken into consideration. It is therefore preferred thatthe wafer loading unit 41 and wafer unloading unit 42 are, as they arein this embodiment, positioned separately from the two polishing bases.Namely, it is preferred that a supply route along which unpolishedwafers are supplied and a collection route along which polished wafersare collected are defined mutually independently.

For example, for improving a throughput offered by a CMP machine capableof carrying out rough polishing and fine polishing, another polishingbase may be positioned at the wafer unloading unit 42 and a total ofthree polishing bases may be used for rough polishing and finepolishing. Two of the polishing bases may be used for polishingrequiring a long processing time. In this case, four receiver membersincluding two loading receiver members and two unloading receivermembers are formed in a wafer transfer unit. Any two of the fourreceiver members can be selected by rotating the wafer transfer unit ormoving it parallel. Thus, the loading receiver members and unloadingreceiver members can be used independently. By adopting this structure,it can be prevented that polishing precision deteriorates due to dustsuch as abrasive particles or leavings adhering to the back of anunpolished wafer. However, even in this case, separate transportationarms are needed to transport wafers to the loading receiver members andunloading receiver members respectively. The transportation arms musttherefore be located so that they will access the receiver members fromdifferent directions. Accordingly, the associated layer thicknessmeasuring instrument and washer must be positioned in differentdirections. This leads to a wide bay. Besides, this structure iseffective only when the time required for rough polishing is differentfrom the time required for fine polishing to such an extent that onetime is twice as long as the other. As far as the times required forrough polishing and fine polishing are almost the same, the adoption ofthe structure does not lead to an improved throughput. Incidentally, inthe present embodiment, the times required for rough polishing and finepolishing are the same. In this case, the layout of components inaccordance with the present invention is preferable.

INDUSTRIAL APPLICABILITY

According to the present invention, a CMP machine to be runautomatically can offer a high throughput and ensure high polishingprecision. Moreover, a layout of components requiring a small area forinstallation, or especially, a small bay can be realized.

What is claimed is:
 1. A wafer polishing machine, comprising: first andsecond polishing bases each having a polishing cloth attached to thesurface thereof and rotating the polishing cloth; first and second waferholding heads each holding wafers and rotating while pressing thesurfaces of the wafers against said polishing cloth; a wafer loadingunit on which unpolished wafers are placed; a wafer unloading unit onwhich polished wafers are placed; a first head rotating mechanism forrotating said first wafer holding head so as to position it above saidfirst polishing base, wafer loading unit, or wafer unloading unit; asecond head rotating mechanism for rotating said second wafer holdinghead so as to position it above said second polishing base, waferloading unit, or wafer unloading unit; a first transportation mechanismfor transporting an unpolished wafer to said wafer loading unit; and asecond transportation mechanism for transporting a polished wafer fromsaid wafer unloading unit, wherein the first transportation mechanismand the second transportation mechanism are different, wherein saidfirst and second polishing bases are located mutually adjacently, saidwafer loading unit and wafer unloading unit are located mutuallyadjacently, said first polishing base and wafer loading unit are locateddiagonally, and said second polishing base and wafer unloading unit arelocated diagonally.
 2. A wafer polishing machine according to claim 1,wherein said first and second wafer holding heads can mutuallyindependently rotate while holding two respective wafers.